Electrically forming tubular shapes



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AT TGRNE Y Sm@ Il Patented Apr. 4, 1944 UNITED STATES yPATENT anni FFHCE ELECTRICALLY soaMING 'rheuma shares Williaml C. Heath, Shorewood, Wis., assigner to iA. O. Smith Corporation, Milwaukee, Wis., a corporation of New York Application November Si), 1942, Serial No. 467,345 fz claims. (ci. 21a-ei Westin and Axel Westin, Serial No. 376,669, :tiled January 3l), 1941, for improvementin Method oi treating metallic bodies, now Patent No. 2,309,561, dated January 26, 1943.

The invention has been applied in the manue facture of airplane struts of tapered or conical shape where the inside surface oi the strut is smooth and devoid of scratches or defects that might cause failure from fatigue. The inverntion may be applied to the upsetting of tube ends and to the forming ci various tubular shapes.

The principal object of the invention is to electricaliy heat and form the blanks and to iron out undesirable variations in thickness without injuring or scratching the inside surface oi the blanks.

Another object of the invention is to facilitate the' rotation of the blank in the forming die and substantialy retard the tendency of the blank to twist spiraliy.

@ther objects will appear in connection, with a L.

...supported concentrically within the blank.

'The mandrel 3 has its large end secured to the chuck and is of a diameter approximating the inside diameter of the blank l. The small end of the mandrel 3 extends axially out of the free end of the blank.

The forging die l is disposed in axial alignment with the ireeend of the blank and mandrel and comprises a plurality of electrode die segments cireumferentially separated along longitudinal lines and connected by leads 5 to a suitable source 6 or heating current.

The inside forming surface of the die 4 is conlcally-shaped with the end of largest diameter constituting the mouth of the die and having a' diameter suflicient to receive the blank `I as the latter is fed longitudinally into the die and rotated by the chuck 2.

As the blank l moves into pressure Contact with the electrode dies, heating current is passed' through successive circumerentially adjacent areas of the blank in recurrent cycles. As the end portion of the blank softens by heat the blank is gradually fed into the die resulting in the progressive heating and forming of the blank until the cone i is completed as shown in' Fig. 2. In the last stages of the'iorming operation the mandrei 3 contacts the inside siiriace of the blank and, rotating therewith, tends te press theblank uniformly against the die so as to iron out any unevenness in thickness that may exist.

The taper oi the mandrel t and oi' the inside surface of die i may he the same so w to obtain a more nearly uniformly thick cone. However, it is preferabie in making of struts and the like to provide a slightly steeper taper for the mandrel to compensate and allow at least in part for the tendency ci? the blank to thicken at the smaller end of the cone.

'By having the mandrel rotate with the blank there is less tendency tor friction therebetween and ier scratching ci the interior surta-ce oi' the The free end oi the hlank aise has liess tendency to twist under the friction ci die since as soon as the mandrel comes into contact with the blank it supports it and strengthens against twisting. As a result the blank is more uniformly shaped. Where the form oi.' 'the article being produced is such that thev mandrel is in contact with the blank for a longer period this advantage becomes more pronounceati.` Movement of th mandrel longitudinally resulting from a further feeding of the blank into the die Y"after the mandrel first contacts with the inside surface of the blank substantially evens out any irregularity in thickness in the blank.

The invention is applicable as an improvement upon that set forth in the copending application of William E. Crawford, Serial No. 566,135, filed November 19, 1942, for Apparatus for electrically upsetting pipe ends, now Patent No. 2,325,480,

dated July 27, 1943. In such application of the present invention, the'rotation of the mandrel with the blank serves to facilitate the formin of an upset end on pipe.

Various embodiments of the invention may be employed within the scope of the accompanying claims.

The `invention is claimed as follows:

1. The improvement in the process of the class described which comprises employing an inter- 'nal mandrel for supporting a tubular blank against the forming operation of an external die,

and rotating rthe mandrel withthe blank as the latter enters the electrode dies to prevent injury to their/mer surface of the blank during forming i andcbtain a more uniform shaping of the blank.

2. The improvement in the process of the class ,described which comprises rotating and feed ing an internal supporting mandrel with the blank into the tubular electrode dies.

3. In apparatus of the class described, a die having a plurality of electrode die segments connected to a source of heating current, an internal die member forming with said die a die cavity 'with said die a die cavity for receiving and forming the end of a tubular blank, means to rotate a tabular blank and reed the same into said die cavity to heat and form the blank, and means to rotate said internal die member with said blank.

5. En apparatus cf the class described. a die having a plurality of electrode die segments connected to a source of heating current and defining the outer surface of a die cavity, a man-1 drel for co-operating with said die and forming the inner surface of the die cavity, means to rotate and feed a tubular blank into said die cavity, and means to rotate said mandrel.

6. In apparatus of the class described, a die having a plurality of electrode die segments connected to a source of heating current and defining the outer surface of a die cavity, a mandrel for cooperating with said die and forming the inner surface of the die cavity, and means to rotate and feed said mandrel 'and a tubular blank surrounding the same into said die to form the blank. A

7. In apparatus of the class described, a die providing a circular cavity conned externally and internally for receiving the end of a rotating tubular blank to form the same, one of the conning surfaces constituting a plurality of electrode die segments spaced circumferentially to supply heating current to the blank during forming, and the other conning surface of the die being disposed to rotate and advance with the blank to thereby support the same against forming pressures.

' WELIAM C. HEATH. 

